It has been demonstrated that immature and maturating neurons are morphologically and physiologically different from mature neurons (Noback and Purpura, 1961, Voeller et al 1963, Purpura 1961, Rose and Ellingson 1971). Due to the paucity of experimental anatomical studies of the mammalian nervous system during this period of ontogeny, 1) many of these changes have previously not been determined and 2) structural correlates associated with the functional changes have not been ascertained. In this context, Laemle, Benhamida, and Purpura, 1972, in the first experimental degeneration study of its kind, demonstrated that the geniculocortical projections are organized differently in the immature and the mature cortex. In the neonatal and postnatal kitten lesions of the lateral geniculate nucleus produce degeneration predominantly in superficial layers of the visual cortex. In the adult, such lesions result in degeneration predominantly in layer IV of the visual cortex. These results are consistent with observations on the changing electrographic characteristics of primary visual evoked potentials during postnatal development. (Rose, 1971). The proposed project is based upon the hypothesis that the lateral geniculate nucleus is not unique in the immaturity of its fiber connections at birth, but that other components of the visual pathway are likewise immature. Lesions will be placed in the optic nerve, lateral geniculate nucleus pars dorsalis and pars ventralis, pretectal region, superior colliculus, and visual cortex of kittens ranging in age from newborn to one month of age and in adult cats. The animals will be sacrified at various intervals post-operatively by intracardiac perfusion under nembutal anesthesia. Resulting degeneration in the visual pathways will be studied by light (Fink-Heimer) and electronmicroscopic techniques. Normal morphology of the subcortical visual centers will also be studied. It is the primary aim of this project to determine the normal morphology of the components of the immature visual system and to establish their connections. It is furthermore, the aim of this project to determine at what point the visual pathways as we know them in the adult are defined and to relate anatomical data concerning ontogenesis of this system to physiological and behavioral data.